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  • Open Access


    Using the Discontinuous Deformation Analysis to Model Wave Propagations in Jointed Rock Masses

    Y.J. Ning1,2,3, Z.Y. Zhao3, J.P. Sun3, W.F. Yuan1,2

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.3, pp. 221-262, 2012, DOI:10.3970/cmes.2012.089.221

    Abstract In this paper, wave propagations in jointed rock masses are modeled by the discontinuous deformation analysis (DDA) method. The selection of the numerical control parameters in the DDA for wave propagation modeling is discussed in detail, and the effects of the joint stiffness, the seismic loading frequency, the joint strength, and the incident angle on the propagations of stress waves in a jointed rock mass are modeled and analyzed. Two nonreflecting boundary conditions including the viscous boundary condition (VBC) and the superposition boundary condition (SBC) are coupled into the DDA. The applicability of the two nonreflecting boundary conditions for simple… More >

  • Open Access


    High-order Alternating Direction Implicit Method Based on Compact Integrated-RBF Approximations for Unsteady/Steady Convection-Diffusion Equations

    N. Thai-Quang1, N. Mai-Duy1, C.-D Tran1, T. Tran-Cong1

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.3, pp. 189-220, 2012, DOI:10.3970/cmes.2012.089.189

    Abstract In this paper, the alternating direction implicit (ADI) method reported in [You(2006)] for the convection-diffusion equation is implemented in the context of compact integrated radial basis function (CIRBF) approximations. The CIRBF approximations are constructed over 3-point stencils, where extra information is incorporated via two forms: only nodal second-order derivative values (Scheme 1), and both nodal first- and second-order derivative values (Scheme 2). The resultant algebraic systems are sparse, especially for Scheme 2 (tridiagonal matrices). Several steady and non-steady problems are considered to verify the present schemes and to compare their accuracy with some other ADI schemes. Numerical results show that… More >

  • Open Access


    Predicting Leakage-induced Settlement of Shield tunnels in Saturated Clay

    D.M. Zhang1,2, L.X. Ma1,2, H.W. Huang1,2, J. Zhang1,2

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.3, pp. 163-188, 2012, DOI:10.3970/cmes.2012.089.163

    Abstract This paper suggests a new set of analytical solutions for predicting leakage-induced seepage field and ground settlement in saturated clay. A unique feature of the solutions presented is considering the effect of the tunnel lining through the relative permeability between the tunnel and the soil. Through the superposition method, the proposed method can be easily extended to twin parallel tunnels. The accuracy of the analytical solutions are verified with numerical simulations. Parametric studies reveal that the decrease of pore pressure and the consequent settlements of ground and tunnel is proportional to the relative permeability. Over 20% of the initial hydrostatic… More >

  • Open Access


    On Improving the Accuracy of Prediction of the Down-hole Drag & Torque in Extended Reach Drilling (ERD)

    Deli Gao1,2, Lianzhong Sun1,3, Hongshu Wei4, Shunwen Wang4

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.2, pp. 143-162, 2012, DOI:10.3970/cmes.2012.089.143

    Abstract Due to the complexity of forces acting on the down-hole tubular strings in extended reach drilling (ERD), the factors which influence the process should be taken into account as much as possible, in order to predict the down-hole drag & torque more accurately. This can help us to identify and prevent the problems related to downhole drag & torque in ERD. The effects of such factors, as the tubular buckling, the buoyancy, the mechanical resistance and the friction reducer, on down-hole drag & torque, are taken into account in this paper, in order to improve the accuracy of the prediction… More >

  • Open Access


    On the Use of PEBI Grids in the Numerical Simulations of Two-Phase Flows in Fractured Horizontal Wells

    Yongsheng An1, Xiaodong Wu1, Deli Gao1

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.2, pp. 123-142, 2012, DOI:10.3970/cmes.2012.089.123

    Abstract The accuracy of numerical simulation of a two-phase (oil and water) flow in a fractured horizontal well depends greatly upon the types of grids used in the computation. Cartesian grids have been widely used in recent years, but they have some disadvantages in describing complex structural wells, such as fractured horizontal wells. For example, Cartesian grids are not efficient in describing the main wellbores and the fractures of fractured horizontal wells, and the results can frequently suffer from grid orientation effects, even though a grid-refinement is often introduced to enhance the adaptability of a Cartesian grid. The PEBI (Perpendicular Bisector)… More >

  • Open Access


    On Appropriately Matching the Bottomhole Pendulum Assembly with the Anisotropic Drill Bit, to Control the Hole-Deviation

    Deli Gao1, Zhen Dong1, Hui Zhang1

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.2, pp. 111-122, 2012, DOI:10.3970/cmes.2012.089.111

    Abstract The bottom hole pendulum assembly is a type of bottom hole assembly (BHA) for controlling the hole deviation, and has been widely used in drilling engineering. Generally, the ability of the drill bit to penetrate laterally, is different from its ability to penetrate axially, so that the drill bit has an anisotropy which affects the hole-deviation-control characteristics of the BHA. The tilt angle and the side force of the drill bit are obtained by a BHA analysis based on the method of weighted residuals. Thus, the effective drilling force can be determined using the rock-bit interaction model. On this basis,… More >

  • Open Access


    An Analysis of The Flow Resistance in Coiled Tubing Wound Around A Reel, In Microhole Drilling

    Xuejun Hou1,2, Deli Gao1, Zhonghou Shen1

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.2, pp. 97-110, 2012, DOI:10.3970/cmes.2012.089.097

    Abstract Microhole drilling (MHD) is a new frontier drilling technology in which the diameter of wellbore is less than 88.9mm and coiled tubing (CT) is used as drill string. The CT wound around reel for MHD has small bending radius and large length to result in large circulating flow resistance and affect normal MHD circulation. The calculation model for curvature radius and length of CT wound around reel are established by analyzing the relationships among the various geometrical parameters of the reel system. The calculation model is combined with Dean number and power-law fluid state equation to put forward the calculation… More >

  • Open Access


    Distribution of the Sizes of Rock Cuttings in Gas Drilling At Various Depths

    Jun Li1, Shunji Yang1, Boyun Guo1,2, Yin Feng2, Gonghui Liu1,3

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.2, pp. 79-96, 2012, DOI:10.3970/cmes.2012.089.079

    Abstract In the process of gas drilling, the mechanism of transport of the cuttings up the annulus is significant, because it controls the minimum amount of volume of the required gas, the cost of cleaning the borehole, the stability of the borewell and the drill pipe erosion, etc. However, current studies in this area are only limited to theoretical discussions. The reason why drill cuttings are of very fine sizes , in air drilling, is believed to be due to the repeated crushing action of drill bit at the bottom of the hole, and the collision between cuttings themselves and the… More >

  • Open Access


    A Study on the Stability of the Borehole in Shale, in Extended-reach Drilling

    Baohua Yu1, Chuanliang Yan1, Deli Gao1,2, Jinxiang Li3

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.1, pp. 57-78, 2012, DOI:10.3970/cmes.2012.089.057

    Abstract Shale is easy to hydrate and often causes a collapse of the borehole during drilling, especially in drilling extended-reach wells (ERW). In order to solve the problem of collapse of the shale, the changinges in the mechanical properties of shale, as affected by hydration and water absorption, are studied in this paper, through experiments. The relationships between the mechanical properties of shale and the water content are established. The borehole-stability models, which couple chemistry and mechanics are established, by considering the anisotropy of swelling, based on the experimental results. The stability of shale in the borehole is analyzed to obtain… More >

  • Open Access


    A Method for the Detection of the Distance & Orientation of the Relief Well to a Blowout Well in Offshore Drilling

    Cui Li1, Deli Gao1, Zhiyong Wu1, Binbin Diao1

    CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.1, pp. 39-56, 2012, DOI:10.3970/cmes.2012.089.039

    Abstract At present, a relief well is the most reliable method to control serious blowout accidents, and it is necessary to detect very accurately the relative position of the relief well and the blowout well. The detection tool should be capable of detecting directly the relative distance and direction between the relief well and the blowout well. Its detection accuracy should also meet the engineering demand of drilling a relief well. Using the working principle of a proposed detection tool, this paper analyzes the spread and attenuation laws of the current injected by a single-electrode or three-electrode array in the relief… More >

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